1. Field of the Invention
The present invention relates generally to an apparatus and method for scanning and, more particularly, to adjusting the airflow of a cooling unit in an image scanning apparatus.
2. Description of the Related Art
Photographs, transparencies, documents and other images are often electronically scanned to produce a digital representation of the image. Typically, the image is scanned with light in order to generate a digital representation of the image.
A simple flatbed scanner consists of an enclosure and an image capture device that is often referred to as the scanhead. One example of an image capture device is a charge-coupled device module (CCDM). The CCDM contains, among other items, an illumination assembly with one or more than one lamps to provide a light source for capturing the image. Hereafter, for simplicity, we use the lamp to refer to the illumination assembly which may include its driving circuitry such as in the form of an electronic inverter. The lamp dissipates heat as expected and the heat generated varies across lamp designs. It is commonly desired for the lamp to provide “instant on” capability to reduce the time for first scan or copy. An example of this type of lamp is external electrode xenon fluorescent lamps. In a scanner using xenon fluorescent lamp at the higher illuminance required to meet an image scanning apparatus with a high image forming speed, the xenon fluorescent lamp is often heated to a high temperature due to its relatively lower energy to light conversion efficiency. Another component of the CCDM is the sensor itself which is typically mounted to a printed circuit board (PCB) that is mounted to the CCDM. It is important that the heat from the lamp does not affect the image capture unit, its optical system, or electrical components of the printed circuit board.
In the prior art a typical solution as shown in FIG. 1 is to introduce a cooling unit such as a fan to direct airflow across the lamp thereby effectively cooling the lamp and carrying the heat away from the critical components of the image capture unit and printed circuit board. However, in order for the lamp to operate correctly the temperature distribution from one end to the other end should not vary by more than a predefined temperature limit. In the preferred embodiment of the present invention, this temperature difference is 30 degrees C. The typical design that incorporates a fan does not provide even cooling of the lamp and while it is possible for additional fans to be used, the use of additional fans results in higher production cost and creates other airflow issues. Additionally, a fan introduces contamination into the scanner by blowing air from the outside into the scanner chamber that houses the image capture unit. While a filter can be placed on the fan, inevitably some contaminants pass through and are introduced into the scanner along with ambient air. The optics of the image capture unit are very sensitive to contaminants which gather around the location of the optical path near the document plane or near the sensor array producing objectionable vertical lines on the scanned document. Further, when contaminants gather in other locations of the optical path of the image capture unit optics, an undesirable scattering that decreases the contrast and resolution of the scan.
Thus, there is still a need for a single fan to effectively and evenly cool the lamp as well as the critical components of the printed circuit board and the optical components of the image capture unit. Further, the fan needs to direct contamination away from the image capture unit in order to avoid image defects that affect the image quality of the image scanning apparatus.